Installing ice-melting cable on old metal roof

So I have an issue with ice and snow sliding off my 95 year old roof into my neighbor's driveway. The only way I can solve this is to either install ice-melting cables or extend the height of his fence by 4 feet.

If I'm to go with the ice-melting cable route, what is the best way to install the clips to hold the cables into a metal roof without causing damage and leaks? Would a sheet-metal screw with a bonded rubber washer do the job? It's too cold to apply any sort of caulking and have it set properly.

I'm not a fan of the idea of screwing into a roof that has gone this long without leaking. Extending the fence would likely be easier and cheaper. Any suggestions or ideas would be greatly appreciated.